In a cellular radio network, base stations continuously broadcast information about themselves and their environment. Such information may include, for example, a location area identifier, base station identifier, base station type, and so-called neighbouring cell information. When a mobile station is registered in the base station of a certain cell, it monitors the quality of the transmission of the neighbouring base stations and changes to one of these neighbouring base stations if the quality of the transmission of the present base station becomes low enough. A cellular radio network must usually have information on the roaming of a mobile station within the network radio coverage area with an accuracy of a so-called location area, which comprises a suitable number of predetermined cells and their base stations. In connection with the updating of the location of a mobile station, the identifier of this location area will be stored in the subscriber data bases in the network. The location data of the subscriber indicates thus a physical and geographical area within the radio coverage area of the cellular radio network. The location area information broadcast by a base station informs a mobile station of the location area to which the base station belongs. When the mobile station moves to another cell within the same location area, location updating to the cellular radio network is not needed, i.e. the location data does not change. However, when the mobile station, on the basis of location area information, observes that the location area changes with the new base station, it starts location updating by sending a location updating request to the cellular radio network. As a result of this location updating request, the cellular radio network updates the location data of the subscriber with the identifier of the new location area.
The system described above operates well in a conventional network. In the future, however, a fixed cellular radio network area may comprise mobile radio exchanges or systems disposed e.g., on trains, ships or possibly even aeroplanes to serve mobile stations used by passengers. Such systems are also called MCPNs (Mobile Customer Premises Networks). When such a mobile system moves, for instance on a Train, from one physical location area to another in a fixed cellular radio network, a large number of mobile stations registered in the mobile radio system effect location updating to the cellular radio network. This leads to a considerable signalling load in the cellular radio network.
Finnish Patent Application No. 913 217 discloses location updating when a DECT (Digital European Cordless Telecommunications) system, whose subscribers are also subscribers of the GSM system, roams in a GSM cellular system. When the DECT system roams from one GSM location area to another, a complicated procedure is followed to update in the GSM network the location data of all subscribers registered in the DECT system, which causes a considerable signalling load.